Orexin

Orexin, also called hypocretin, is a neurotransmitter that regulates arousal, wakefulness, and appetite. The most common form of narcolepsy, in which the sufferer briefly loses muscle tone (cataplexy), is caused by a lack of orexin in the brain due to destruction of the cells that produce it.

The brain contains very few cells that produce orexin: in a human brain, about 10,000 to 20,000 neurons in the hypothalamus. However, the axons from these neurons extend throughout the entire brain and spinal cord, where there are also receptors for orexin.

Orexin was discovered almost simultaneously by two independent groups of rat-brain researchers. One group named it orexin, from orexis, meaning "appetite" in Greek; the other group named it hypocretin, because it is produced in the hypothalamus and bears a weak resemblance to secretin, a hormone found in the gut. The scientific community has not yet settled on a consensus for which word to use.

Read more about Orexin:  Isoforms, Function, History and Nomenclature, Selective Ligands, Interaction With Other Neurotransmitter Systems

Other articles related to "orexin, orexins":

Orexin-A - Ongoing Research
... The test group was administered orexin-A intravenously, or nasally ... monkeys, which were given the nasal form of orexin-A, performed far better than the ones treated with injections ... Orexin-A not only restored the monkey’s cognitive abilities but made their brains appear awake in PET scans ...
Orexin Receptor
... The orexin receptor (also referred to as the hypocretin receptor) is a G-protein-coupled receptor that binds the neuropeptide hormone orexin ... Both orexin receptors exhibit a similar pharmacology - the 2 orexin peptides, orexin-A and orexin-B, bind to both receptors and, in each case, agonist binding results in an increase in intracellular calcium levels ... However, orexin-B shows a 10-fold selectivity for orexin receptor type 2, whilst orexin-A is equipotent at both receptors ...
Orexin - Interaction With Other Neurotransmitter Systems
... Orexins act on Gq-protein-coupled receptors signaling through phospholipase C (PLC) and calcium-dependent as well as calcium-independent transduction pathways ... Postsynaptic actions of orexins on their numerous neuronal targets throughout the CNS are almost entirely excitatory ...
Orexin-A - Effects of Supplementation
... To date, orexin-A has shown no negative side effects ... Taking orexin-A also increases arousal, alertness, attention, and muscle tone ... Orexin-A has no effect on subjects who are well rested ...
Wakefulness - Maintenance By The Brain
... Another key system is that provided by the orexins (also known as hypocretins) projecting neurons ... Orexin deficiency has been identified as responsible for narcolepsy ... Research suggests that orexin and histamine neurons play distinct, but complementary roles in controlling wakefulness with orexin being more involved with wakeful behavior and histamine cognition and activation of ...